Thought I would start a new thread showing what and how I stopped my o-ring leak below the thermostat, between the manifold and timing cover.
to prepare: I ran a tap through all holes with threads that were exposed when I removed and disassembled the manifold. This included buying a 3/8" pipe tap and cleaning the threads of the nipple for the heater hose. All flat gasket surfaces were scraped clean with a putty knife and then gone over with a really fine mill file that was completely flat with the surface. this was done with little to no pressure on the file. I purchased new gaskets, o-ring, thermostat housing and 3/8" threaded heater hose nipple. I did not replace the thermostat as it was replaced when I did a valve job on the engine and it has literally zero miles on it.
Assembly: I wrapped two layers of teflon tape counter clockwise so the end of the tape is not pushed by the installation process. I also add a little bit of teflon pipe dope on top of the tape, very light coating. This is probably not needed but makes me feel better. I have plumbed many fittings this way with never a leak. Then I carefully installed it in the freshly chased hole. I applied a thin layer of RTV gasket sealer to both surfaces of the gasket that seals the thermostat and installed the two bolts into the chased bolt holes. I then applied RTV to one side of the gaskets that go against the heads and put bolts in the holes to align them properly. Then I went into the house and ate two chocolate chip cookies as the RTV setup. (I really did) I returned to the shop and put a thin layer of RTV on the manifold surfaces that will press up against
the gaskets on the heads and installed the bolts which I had cleaned with my wire wheel on a bench grinder (the most used tool in my shop)
I then connected the radiator hose, gas line to carb, and the rubber cap that is temporarily closing off the heater hose. I glued the gaskets to the heads with RTV and let it setup so make it easier to align the gaskets and get four bolts in place instead of having gaskets sliding around.
Results: After adding antifreeze (never add just water, that has caused me to crack a block because I forgot I had not added antifreeze and the outside temperature dropped to the low twenties) I fired her up to move her outside so my new garage doors could be installed. Later I had a little leak from the radiator hose and maybe the thermostat gasket. I tightened everything again and all leaks stopped. I checked this morning and no leaks. I did two things in the process that I don't believe in, but seemed to be necessary. First I don't think a gasket is doing its job if I have to add RTV to keep it from leaking. Second it really goes against my grain to use RTV on an o-ring, I usually use silicone and that is all. However, it seems to have worked using both of these methods in this situation.
